Image decoding apparatus and method for handling intra-image predictive decoding with various color spaces and color signal resolutions

ABSTRACT

The present invention is directed to an image information decoding apparatus adapted for performing intra-image decoding based on resolution of color components and color space of an input image signal. An intra prediction unit serves to adaptively change block size in generating a prediction image based on a chroma format signal indicating whether resolution of color components is one of 4:2:0 format, 4:2:2 format, and 4:4:4 format, and a color space signal indicating whether color space is one of YCbCr, RGB, and XYZ. An inverse orthogonal transform unit and an inverse quantization unit serve to also change orthogonal transform technique and quantization technique in accordance with the chroma format signal and the color space signal. A decoding unit decodes the chroma format signal and the color space signal to generate a prediction image corresponding to the chroma format signal and the color space signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/318,491, filed Dec. 30, 2008, now U.S. Pat. No. 7,912,301, which is acontinuation of U.S. application Ser. No. 10/527,922, filed Mar. 16,2005, now U.S. Pat. No. 7,492,950. Application Ser. No. 10/527,922 isthe U.S. National Stage of International Application No. PCT/JP04/10317,filed Jul. 20, 2004, which claims priority to Japanese PatentApplication No. JP 2003-277128, filed Jul. 18, 2003. The contents ofeach of the above-listed applications are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to an image information encoding apparatusand a method therfor, and an image information decoding apparatus and amethod therfor, which are used in receiving, through network media suchas satellite broadcasting service, cable TV (television) or Internet,etc., or in processing with a processor, on storage or memory media suchas optical disc, magnetic disc or flash memory, or other suchnon-transitory computer-readable storage, image compressed information(bit stream) compressed by orthogonal transform such as discrete cosinetransform or Karhunen-Loeve transform, etc. and motionprediction/compensation like MPEG (Moving Picture Experts Group), H.26x, etc.

BACKGROUND ART

In recent years, apparatuses in conformity with the system such as MPEGin which image information are dealt as digital information to compresssuch image information by orthogonal transform such as discrete cosinetransform, etc. and motion prediction/compensation by utilizingredundancy specific to image information for the purpose of realizingtransmission/storage of information having high efficiency in thatinstance are being popularized at both information distribution(delivery) at broadcasting station, etc. and information reception ingeneral homes.

Particularly, the MPEG2 (ISO/IEC 13818-2) is defined as general purposeimage encoding system, and is widely used at present in broadapplication for professional use purpose and consumer use purpose at thestandard where both interlaced scanning image and sequential scanningimage, and standard resolution image and high definition image arecovered. By using the MPEG2 compression system, in the case ofinterlaced scanning image of the standard resolution having, e.g.,720×480 pixels, code quantity (bit rate) of 4 to 8 Mbps is assigned, andin the case of interlaced scanning image of high resolution having1920×1088 pixels, code quantity (bit rate) of 18 to 22 Mbps is assignedso that high compression factor and satisfactory picture quality can berealized.

The MPEG2 is mainly directed to high picture quality encoding adaptedmainly to encoding system for broadcast, but did not comply withencoding system having code quantity (bit rate) lower than that of theMPEG1, i.e., compression factor higher than that. However, it is deemedthat needs of such encoding system will be increased in future withpopularization of portable (mobile) terminals. In correspondencetherewith, standardization of the MPEG4 encoding system has beenperformed. In connection with the image encoding system, its standardhas been approved as the International Standard as ISO/IEC 14496-2 onDecember, 1998.

Further, in recent years, with realization of image encoding fortelevision conference being as the object in the beginning,standardization of H.264 (ITU-TQ6/16 VCEG) is being developed. It isknown that while the H.264 requires a larger number of operationquantities for encoding/decoding thereof as compared to the conventionalencoding system such as MPEG2 or MPEG4, higher encoding efficiency canbe realized. In addition, standardization in which functions whichcannot be supported by H.264 are also taken in with the H.264 being asbase to realize higher encoding efficiency is being performed at presentby JVT (Joint Video Team) as a part of activity of the MPEG4.

Here, outline of the configuration of an image information encodingapparatus adapted for realizing image compression by orthogonaltransform such as discrete cosine transform or Karhnen-Loueve transform,etc. and motion prediction/compensation is shown in FIG. 1. As shown inFIG. 1, the image information encoding apparatus 100 comprises an A/D(Analogue/Digital) converting unit 101, an image sorting buffer 102, anadder 103, an orthogonal transform unit 104, a quantization unit 105, areversible encoding unit 106, a storage buffer 107, an inversequantization unit 108, an inverse orthogonal transform unit 109, anadder 110, a frame memory 111, a motion prediction/compensation unit112, an intra prediction unit 113, and a rate control unit 114.

In FIG. 1, the A/D converting unit 101 converts an inputted image signalinto a digital signal. The image sorting buffer 102 performs sorting offrames in accordance with GOP (Group of Pictures) structure of imagecompressed information outputted from the image information encodingapparatus 100.

In this example, the image sorting buffer 102 delivers image informationof the entirety of frames to the orthogonal transform unit 104 in regardto images in which intra (intra-image) encoding is performed. Theorthogonal transform unit 104 implements orthogonal transform such asdiscrete cosine transform or Karhnen-Loueve transform, etc. to imageinformation to deliver transform coefficients to the quantization unit105. The quantization unit 105 implements quantization processing to thetransform coefficients which have been delivered from the orthogonaltransform unit 104.

The reversible encoding unit 106 implements reversible encoding such asvariable length encoding or arithmetic encoding, etc. to the quantizedtransform coefficients to deliver the encoded transform coefficients tothe storage buffer 107 to store them thereinto. The encoded transformcoefficients thus obtained are outputted as image compressedinformation.

The behavior (operation) of the quantization unit 105 is controlled bythe rate control unit 114. Moreover, the quantization unit 105 deliversquantized transform coefficients to the inverse quantization unit 108.The inverse quantization unit 108 inverse-quantizes the transformcoefficients thus delivered. The inverse orthogonal transform unit 109implements inverse orthogonal transform processing to theinverse-quantized transform coefficients to generate decoded imageinformation to deliver the information thus generated to the framememory 111 to store them thereinto.

On the other hand, the image sorting buffer 102 delivers imageinformation to the motion prediction/compensation unit 112 in regard toimages in which inter (inter-image) encoding is performed. The motionprediction/compensation unit 112 takes out image information referred atthe same time from the frame memory 111 to implement motionprediction/compensation processing thereto to generate reference imageinformation. The motion prediction/compensation unit 112 delivers thereference image information thus generated to the adder 103. The adder103 converts the reference image information into a difference signalbetween the reference image information and the image information thusdelivered. In addition, the motion compensation/prediction unit 112delivers motion vector information to the reversible encoding unit 106at the same time.

The reversible encoding unit 106 implements reversible encodingprocessing such as variable length encoding or arithmetic encoding, etc.to the motion vector information thus delivered to form informationinserted into the header portion of the image compressed information. Itis to be noted that since other processing are the same as those ofimage compressed information to which intra-encoding is implemented,their explanation will be omitted.

Here, in the encoding system in which standardization is performed bythe above-described JVT (hereinafter referred to as JVT Codec), there isemployed intra-predictive encoding such that predictive images aregenerated from pixels around block in performing intra-encoding toencode difference therebetween. Namely, in regard to images in whichintra-encoding is performed, prediction images are generated from pixelvalues in which encoding has been already completed in the vicinity ofpixel block to be encoded so that differences with respect to thepredictive images thereof are encoded. The inverse quantization unit 108and the inverse orthogonal transform unit 109 respectivelyinverse-quantize and inverse-orthogonally transform intra-encodedpixels. The adder 110 adds output of the inverse orthogonal transformunit 109 and prediction images used in encoding pixel blockcorresponding thereto to deliver the added values thus obtained to theframe memory 111 to store them thereinto. In the case of pixel block tobe intra-encoded, the intra prediction unit 113 reads out alreadyencoded neighboring pixels stored in the frame memory 111 to generateprediction image. At this time, also with respect to theintra-prediction mode used for generation of prediction image,reversible encoding processing is implemented thereto at the reversibleencoding unit 106 to output information thus processed in the stateincluded into image compressed information.

Subsequently, outline of the configuration of an image informationdecoding apparatus corresponding to the above-described imageinformation encoding apparatus 100 is shown in FIG. 2. The imageinformation decoding apparatus 120 comprises, as shown in FIG. 2, astorage buffer 121, a reversible decoding unit 122, an inversequantization unit 123, an inverse orthogonal transform unit 124, anadder 125, an image sorting buffer 126, a D/A (Digital/Analogue)converting unit 127, a motion prediction/compensation unit 128, a framememory 129, and an intra-prediction unit 130.

In FIG. 2, the storage buffer 121 temporarily stores inputted imagecompressed information thereafter to transfer the image compressedinformation to the reversible decoding unit 122. The reversible decodingunit 122 implements processing such as variable length decoding orarithmetic decoding, etc. to the image compressed information on thebasis of a predetermined format for image compressed information todeliver quantized transform coefficients to the inverse quantizationunit 123. Moreover, in the case where corresponding frame isinter-encoded frame, the reversible decoding unit 122 also decodesmotion vector information stored at the header portion of the imagecompressed information to deliver the information thus decoded to themotion prediction/compensation unit 128.

The inverse quantization unit 123 inverse-quantizes quantized transformcoefficients delivered from the reversible decoding unit 122 to deliverthe transform coefficients thus obtained to the inverse orthogonaltransform unit 124. The inverse orthogonal transform unit 124 implementsinverse orthogonal transform such as inverse discrete cosine transformor inverse Karhunen-Loeve transform, etc. to the transform coefficientson the basis of a predetermined format for image compressed information.

Here, in the case where corresponding frame is intra-encoded frame, theimage information to which inverse orthogonal transform processing hasbeen implemented are stored into the image sorting buffer 126, and areoutputted after D/A converting processing at the D/A converting unit127.

On the other hand, in the case where corresponding frame isinter-encoded frame, the motion prediction/compensation unit 128generates reference image on the basis of motion vector information towhich reversible decoding processing has been implemented and imageinformation stored in the frame memory 129 to deliver the referenceimage thus generated to the adder 125. The adder 125 synthesizes thereference image and output of the inverse orthogonal transform unit 124.It is to be noted that since other processing are the same as those ofthe intra-encoded frame, their explanation will be omitted.

In this example, since the intra-predictive encoding system is employedin the JVT Codec, in the case where corresponding frame is intra-encodedframe, the intra-prediction unit 130 reads out image from the framememory 129 to generate prediction image in accordance withintra-prediction mode to which reversible decoding processing has beenimplemented at the reversible decoding unit 122. The adder 125 addsoutput of the inverse orthogonal transform unit 124 and this predictionimage.

The image information encoding apparatus 100 and the image informationdecoding apparatus 120 which have been explained above are disclosed in,e.g., Published Japanese Patent Application No. 2003-023637.

Meanwhile, in the JVT Codec (H.264|MPEG-4 AVC), as described above, inperforming intra-encoding processing, there is employed such an intrapredictive encoding system to generate prediction images from pixelsaround block to encode differences therebetween.

Here, in regard to luminance component, there are used two predictionsystems of intra 4×4 prediction mode where prediction is performed on4×4 pixel block basis and intra 16×16 prediction mode where predictionis performed on 16×16 pixel block (macro block) basis.

On the other hand, in regard to color difference components, predictionsare performed on Cb, Cr respective 8×8 block basis. This predictiveencoding method is the same as that in the intra 16×16 prediction mode,wherein this prediction mode is changed into the prediction mode of 8×8block units. The prediction mode in the intra-predictive encoding ofcolor difference is shown in FIG. 3. As shown in FIG. 3, at the JVTCodec, four prediction modes of

(a) Vertical mode (mode=0)

(b) Horizontal mode (mode=1)

(c) DC mode (mode=2)

(d) Plane Prediction mode (mode=3)

are defined. In accordance with prediction mode having least predictivedifference (residual), prediction image is generated. The technique ofgenerating prediction image in these four prediction modes will beexplained below.

(a) Vertical Mode (Mode=0)

In the Vertical mode, pixels of adjacent upper side block of colordifference block (in the case of 4:2:0 format, upper macro block) ofcolor difference block are copied to allow the pixels thus copied to beprediction image of corresponding block. When pixels of adjacent upperside block are expressed as p[x, −1], prediction image predc of thecolor difference block in this case is represented by the followingformula (1). It is to be noted that this mode can be used only in thecase where adjacent upper side block exists.pred_(c) [x,y]=p[x,−1](x,y=0 . . . 7)  (1)

(b) Horizontal Mode (Mode=1)

In the Horizontal mode, pixels of adjacent left side block of colordifference block (in the case of 4:2:0 format, left macro block) arecopied to allow the pixels thus copied to be prediction image ofcorresponding block. When pixels of adjacent left side block areexpressed as p[−1, y], prediction image predc of the color differenceblock in this case is represented by the following formula (2). It is tobe noted that this mode can be used only in the case where adjacent leftside block exists.pred_(c) [x,y]=p[−1,y](x,y=0 . . . 7)  (2)

(c) DC Mode (Mode=2)

In the DC mode, pixels of adjacent upper and left side blocks of colordifference block are used to allow the mean (average) value thereof tobe prediction image. It is to be noted that in the case where adjacentpixels do not exist, value 128 is used as prediction signal.

Namely, in the case of x, y=0 . . . 3, prediction image predc [x, y] isgenerated by using upper side pixel p[x, −1] and left side pixel p[−1,y] which are adjacent (in this example, x, y=0 . . . 3). Moreparticularly, in four cases of the case (i) where pixel p[x, −1] andpixel p[−1, y] both exist, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, (iii) the case where pixel p[x, −1] doesnot exist and pixel p[−1, y] exists, and (iv) the case where pixel p[x,−1] and pixel p[−1, y] do not both exist, prediction images arerespectively generated in accordance with the following formulas (3) to(6).

$\begin{matrix}{\mspace{20mu}\lbrack 3\rbrack} & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 0}^{3}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right)}\operatorname{>>}{3\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}} & (3) \\{\mspace{20mu}{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right)}\operatorname{>>}{2\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}}} & (4) \\{\mspace{20mu}{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{y^{\prime} = 0}^{3}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right)}\operatorname{>>}{2\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}}} & (5) \\{\mspace{20mu}{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {128\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}}} & (6)\end{matrix}$

Similarly, in the case of x=4 . . . 7, y=0 . . . 3, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=4 . . . 7,y=0 . . . 3). More particularly, in three cases of (i) the case wherepixel p[x, −1] exists, (ii) the case where pixel p[x, −1] does not existand pixel p[−1, y] exists, and (iii) the case where pixel p[x, −1] andpixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (7) to (9).

$\begin{matrix}{\mspace{20mu}\lbrack 4\rbrack} & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{x^{\prime} = 4}^{7}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right)}\operatorname{>>}{2\mspace{14mu}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}} & (7) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{y^{\prime} = 0}^{3}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right)}\operatorname{>>}{2\mspace{14mu}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}} & (8) \\{\mspace{20mu}{{pred}_{c} = {128\mspace{14mu}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)}}} & (9)\end{matrix}$

Similarly, in the case of x=0 . . . 3, y=4 . . . 7, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=0 . . . 3,y=4 . . . 7). More particularly, in three cases of (i) the case wherepixel p[−1, y] exists, (ii) the case where pixel p[x, −1] exists andpixel p [−1, y] does not exist, and (iii) the case where pixel p[x, −1]and pixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (10) to (12).

$\begin{matrix}{\mspace{20mu}\lbrack 5\rbrack} & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{y^{\prime} = 4}^{7}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right)}\operatorname{>>}{2\mspace{14mu}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)}} & (10) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = \left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right)}\operatorname{>>}{2\mspace{14mu}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)}} & (11) \\{\mspace{20mu}{{pred}_{c} = {128\mspace{14mu}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)}}} & (12)\end{matrix}$

Similarly, in the case of x, y=4 . . . 7, prediction image predc [x, y]is generated by using upper side pixel p[x, −1] and left side pixelp[−1, y] which are adjacent (in this example, x, y=4 . . . 7). Moreparticularly, in four cases of (i) the case where pixel p[x, −1] andpixel p[−1, y] both exist, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, (iii) the case where pixel p[x, −1] doesnot exist and pixel p[−1, y] exists, and (iv) the case where pixel p[x,−1] and pixel p[−1, y] do not both exist, prediction images arerespectively generated in accordance with the following formulas (13) to(16).

$\begin{matrix}\lbrack 6\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 4}^{7}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (13) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (14) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 4}^{7}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (15) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = 128}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (16)\end{matrix}$

(d) Plane Prediction Mode (Mode=3)

In the Plane Prediction mode, prediction image is plane-approximatedfrom pixel of left side block (left macro block in the case of 4:2:0format) and pixel of upper side block which are adjacent of colordifference block to allow the prediction image thus obtained to beprediction image of corresponding block. When pixel of left side blockand pixel of upper side block which are adjacent are respectivelyexpressed as p[−1, y] and p[x, −1], prediction image predc of colordifference in this case is represented by the following formula (17).Here, Clip1 indicates that clipping into the range from 0 to 255 isperformed.

$\begin{matrix}\lbrack 7\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {{Clip}\; 1\left( {\left( {a + {b \times \left( {x - 3} \right)} + {c \times \left( {y - 3} \right)} + 16} \right) ⪢ 5} \right)}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 7}}} \right){where}\left\{ \begin{matrix}{a = {16 \times \left( {{p\left\lbrack {{- 1},7} \right\rbrack} + {p\left\lbrack {7,{- 1}} \right\rbrack}} \right)}} \\{b = {\left( {{17 \times H} + 16} \right) ⪢ 5}} \\{c = {\left( {{17 \times V} + 16} \right) ⪢ 5}} \\{H = {\sum\limits_{x^{\prime} = 0}^{3}{\left( {x^{\prime} + 1} \right) \times \left( {{p\left\lbrack {{4 + x^{\prime}},{- 1}} \right\rbrack} - {p\left\lbrack {{2 - x^{\prime}},{- 1}} \right\rbrack}} \right)}}} \\{V = {\sum\limits_{y^{\prime} = 0}^{3}{\left( {y^{\prime} + 1} \right) \times \left( {{p\left\lbrack {{- 1},{4 + y^{\prime}}} \right\rbrack} - {p\left\lbrack {{- 1},{2 - y^{\prime}}} \right\rbrack}} \right)}}}\end{matrix} \right.} & (17)\end{matrix}$

In a manner as stated above, after intra-prediction of color differencecomponent is performed by any one of the four prediction modes togenerate prediction image, a difference signal between current pixelblock and the prediction image is generated at the adder 103. Theorthogonal transform unit 104 applies 4×4 integer transform to thedifference signal of 8×8 blocks on 4×4 pixel block basis. When adifference signal obtained by subtracting prediction image from currentpixel block is expressed as F4×4, 4×4 integer transform is representedby the following formula (18).

$\begin{matrix}\lbrack 8\rbrack & \; \\{{f_{4 \times 4} = {T_{4 \times 4} \times F_{4 \times 4} \times T_{4 \times 4}^{T}}}{where}{T_{4 \times 4} = \begin{pmatrix}1 & 1 & 1 & 1 \\2 & 1 & {- 1} & {- 2} \\1 & {- 1} & {- 1} & 1 \\1 & {- 2} & 2 & {- 1}\end{pmatrix}}} & (18)\end{matrix}$

Further, in the JVT Codec, after 4×4 integer transform is performed, (0,0) coefficients (DC coefficients) of four 4×4 blocks within 8×8 blocksare collected to constitute 2×2 blocks as shown in FIG. 4 to apply 2×2Hadamard transform to the 2×2 blocks. This is because efficiency ofintra-prediction used in color difference is not so high, andcorrelation is still left between (0, 0) coefficients of adjacent 4×4blocks. In order to enhance (increase) encoding efficiency to moredegree by utilizing this correlation, only (0, 0) coefficients of 4×4blocks are collected to constitute 2×2 blocks to apply 2×2 Hadamardtransform thereto. When chroma DC block of 2×2 is expressed as fdc2×2,chroma DC block fdc′ 2×2 after undergone 2×2 Hadamard transform isrepresented by the following formula (19).

$\begin{matrix}\lbrack 9\rbrack & \; \\{{{fdc}_{2 \times 2}^{\prime} = {T_{2 \times 2} \times {fdc}_{2 \times 2} \times T_{2 \times 2}^{T}}}{where}{T_{2 \times 2} = {\frac{1}{\sqrt{2}}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}}} & (19)\end{matrix}$

After integer transform processing, respective coefficients arequantized. When parameter for determining quantization coefficients ofluminance is QPy, parameter QPc for determining quantizationcoefficients of color difference is calculated in a manner as describedbelow.

Namely, first, QPy (which takes value ranging from 0 to 51) to beencoded in image compressed information and offset valuechroma_qp_offset of quantization coefficients of color difference areused to calculate parameter QPi in accordance with the following formula(20). In this case, QPi is caused to undergo clipping into the rangefrom 0 to 51.QPi=QPy+chroma_(—) qp_offset  (20)

Further, this QPi is used to determine parameter QPc of color differencefrom the Table 1 shown as below.

TABLE 1 QP_(i) <30 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 4748 49 50 51 QP_(c) =QP_(i) 29 30 31 32 32 33 34 34 35 35 36 36 37 37 3738 38 38 39 39 39 39

Here, when values of respective AC coefficients before quantization aref, and values of respective AC coefficients after quantization are f′,values of quantized coefficients are represented by the followingformula (21).

$\begin{matrix}\lbrack 11\rbrack & \; \\{{{f^{\prime}\left\lbrack {i,j} \right\rbrack} = {\left( {{{f\left\lbrack {i,j} \right\rbrack} \times {Q\left( {{{QP}_{c}\mspace{14mu}{\% 6}}\;,i,j} \right)}} + r} \right) ⪢ \left( {15 + {{QP}_{c}/6}} \right)}}\left( {i,{j = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right){where}\left\{ \begin{matrix}\begin{matrix}{{{Q\left( {{{QP}\mspace{14mu}{\% 6}},i,j} \right)} = {{{quantMat}\left\lbrack {{QP}\mspace{14mu}{\% 6}} \right\rbrack}\lbrack 0\rbrack}},} & {\left( {i,j} \right) \in \left\{ {\left( {0,0} \right),\left( {0,2} \right),\left( {2,0} \right),\left( {2,2} \right)} \right\}} \\{{= {{{quantMat}\left\lbrack {{QP}\mspace{14mu}{\% 6}} \right\rbrack}\lbrack 1\rbrack}},} & {\left( {i,j} \right) \in \left\{ {\left( {1,1} \right),\left( {1,3} \right),\left( {3,1} \right),\left( {3,3} \right)} \right\}} \\{{= {{{quantMat}\left\lbrack {{QP}\mspace{14mu}{\% 6}} \right\rbrack}\lbrack 2\rbrack}},} & {otherwise}\end{matrix} \\{{{{quantMat}\lbrack 6\rbrack}\lbrack 3\rbrack} = \begin{bmatrix}13107 & 5243 & 8224 \\11651 & 4660 & 7358 \\10486 & 4143 & 6554 \\9198 & 3687 & 5825 \\8322 & 3290 & 5243 \\7384 & 2943 & 4660\end{bmatrix}}\end{matrix} \right.} & (21)\end{matrix}$

On the other hand, when values of respective DC coefficients beforequantization are fdc, and values of respective DC coefficients afterquantization are fdc′, values of quantized coefficients are representedby the following formula (22). In this case, r in the formula (22) isconstant for rounding processing.fdc′[i,j]=(fdc[i,j]×Q(QP _(c)%6,0,0)+r)>>(16+QP _(c)/6)(i,j=0 . . .1)  (22)

Moreover, when AC coefficients after inverse quantization are f″,inverse quantization of AC coefficients is represented by the followingformula (23).

$\begin{matrix}\lbrack 13\rbrack & \; \\{{{f^{\prime}\left\lbrack {i,j} \right\rbrack} = {\left( {{{f\left\lbrack {i,j} \right\rbrack} \times {{IQ}\left( {{{QP}_{c}\mspace{14mu}{\% 6}}\;,i,j} \right)}} + r} \right) ⪡ \left( {{QP}_{c}/6} \right)}}\left( {i,{j = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right){where}\left\{ \begin{matrix}\begin{matrix}{{{{IQ}\left( {{{QP}\mspace{14mu}{\% 6}},i,j} \right)} = {{{iquantMat}\left\lbrack {{QP}\mspace{14mu}{\% 6}} \right\rbrack}\lbrack 0\rbrack}},} & {\left( {i,j} \right) \in \left\{ {\left( {0,0} \right),\left( {0,2} \right),\left( {2,0} \right),\left( {2,2} \right)} \right\}} \\{{= {{{iquantMat}\left\lbrack {{QP}\mspace{14mu}{\% 6}} \right\rbrack}\lbrack 1\rbrack}},} & {\left( {i,j} \right) \in \left\{ {\left( {1,1} \right),\left( {1,3} \right),\left( {3,1} \right),\left( {3,3} \right)} \right\}} \\{{= {{{iquantMat}\left\lbrack {{QP}\mspace{14mu}{\% 6}} \right\rbrack}\lbrack 2\rbrack}},} & {otherwise}\end{matrix} \\{{{{quantMat}\lbrack 6\rbrack}\lbrack 3\rbrack} = \begin{bmatrix}10 & 16 & 13 \\11 & 18 & 14 \\13 & 20 & 16 \\14 & 23 & 18 \\16 & 25 & 20 \\18 & 29 & 23\end{bmatrix}}\end{matrix} \right.} & (23)\end{matrix}$

On the other hand, when inverse-quantized DC coefficients are fdc″,inverse quantization of DC coefficients is represented by the followingformula (24) in the case where QPc is 6 (six) or more, and isrepresented by the following formula (25) in the case where QPc is lessthan 6 (six).fdc″[i,j]=(fdc′[i,j]×IQ(QP _(c)%6,i,j))<<(QP _(c)/6−1)(i,j=0 . . .3)  (24)fdc″[i,j]=(fdc′[i,j]×IQ(QP _(c)%6,i,j))>>1(i,j=0 . . . 3)  (25)

While intra-predictive encoding processing is performed in the JVT Codecin a manner as stated above, there was the problem that even if theabove-mentioned technique is used, since block size is small in theintra-predictive encoding of color difference, encoding efficiency isinferior as compared to luminance.

In addition, there was the problem that the above-mentioned techniqueonly complies with 4:2:0 format and YCbCr color space, so encodingcannot be performed in the case of 4:2:2 format, 4:4:4 format, RGB colorspace, XYZ color space, etc.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been proposed in view of conventional actualcircumstances as described above, and its object is to provide an imageinformation encoding apparatus and a method therefor, and an imageinformation decoding apparatus and a method therefor, which can moreefficiently perform encoding/decoding of even images of 4:2:2 format,4:4:4 format, RGB color space and/or XYZ color space, etc.

Means for Solving the Problems

The image information encoding apparatus according to the presentinvention is directed to an image information encoding apparatus adaptedfor blocking an input image signal to implement orthogonal transformthereto on the block basis to perform quantization, which comprises:intra-image prediction means for adaptively changing block size on thebasis of a chroma format signal indicating resolution of a color signaland a color space signal indicating color space to generate a predictionimage in performing intra-image predictive encoding of the color signal;transform means for performing, on a predetermined block size basis,integer transform of a difference signal between the prediction imagegenerated by the intra-image prediction means and an original image;quantization means for adaptively changing quantization technique inaccordance with transform processing by the transform means to quantizetransform coefficients generated by the transform means; and encodingmeans for encoding the transform coefficients quantized by thequantization means, the chroma format signal and the color space signal.

Moreover, the image information encoding method according to the presentinvention is directed to an image information encoding method ofblocking an input image signal to implement orthogonal transform theretoon the block basis to perform quantization, which comprises: anintra-image prediction step of adaptively changing block size on thebasis of a chroma format signal indicating resolution of a color signaland a color space signal indicating color space to generate a predictionimage in performing intra-image predictive encoding of the color signal;a transform step of performing, on a predetermined block size basis,integer transform processing of a difference signal between theprediction image generated at the intra-image prediction step and anoriginal image; a quantization step of adaptively changing quantizationtechnique in accordance with transform processing at the transform stepto quantize transform coefficients generated at the transform step; andan encoding step of encoding the transform coefficients quantized at thequantization step, the chroma format signal and the color space signal.

In such image information encoding apparatus and method therefor, inperforming intra-image predictive encoding of input image signal, blocksize in generating prediction image is adaptively changed on the basisof chroma format signal indicating whether resolution of color componentis that of any one of 4:2:0 format, 4:2:2 format and 4:4:4 format, etc.,and color space signal indicating whether color space is any one of,e.g., YCbCr, RGB and XYZ, etc. Further, in the image informationencoding apparatus and the method therefor, chroma format signal andcolor space signal are encoded along with quantized transformcoefficients.

Further, the image information decoding apparatus according to thepresent invention is directed to an image information decoding apparatusadapted for decoding information obtained by implementing inversequantization and inverse orthogonal transform to image compressedinformation in which an input image signal is blocked to implementorthogonal transform thereto on the block basis so that quantization isperformed with respect thereto, which comprises: decoding means fordecoding quantized and encoded transform coefficients, a chroma formatsignal indicating resolution of a color signal and a color space signalindicating color space; inverse quantization means for adaptivelychanging inverse quantization technique in accordance with the chromaformat signal and the color space signal to inverse-quantize thetransform coefficients decoded by the decoding means; inverse transformmeans for performing integer transform of the inverse-quantized blocks;and intra-image prediction means for generating a prediction image inperforming intra-image predictive decoding of the color signal at ablock size corresponding to the chroma format signal and the color spacesignal by using an output signal from the inverse transform means.

In addition, the image information decoding method according to thepresent invention is directed to an image information decoding method ofdecoding information obtained by implementing inverse quantization andinverse orthogonal transform to image compressed information in which aninput image signal is blocked to implement orthogonal transform theretoon the block basis so that quantization is performed with respectthereto, which comprises: a decoding step of decoding quantized andencoded transform coefficients, a chroma format signal indicatingresolution of a color signal and a color space signal indicating colorspace; an inverse quantization step of adaptively changing inversequantization technique in accordance with the chroma format signal andthe color space signal to inverse-quantize the transform coefficientsdecoded at the decoding step; an inverse transform step of performinginteger transform of the inverse-quantized blocks; and an intra-imageprediction step of generating a prediction image in performingintra-image predictive decoding of the color signal at a block sizecorresponding to the chroma format signal and the color space signal byusing an output signal of the inverse transform step.

In such image information decoding apparatus and the method therefor,chroma format signal indicating whether resolution of color component isthat of any one of, e.g., 4:2:0 format, 4:2:2 format and format 4:4:4format, etc., and color space signal indicating whether color space isany one of, e.g., YCbCr, RGB, and XYZ, etc. are decoded to generateprediction image in performing intra-image predictive decoding of thecolor signal at a block size corresponding to the chroma format signaland the color space signal.

Effects/Advantages of the Invention

In accordance with the image information encoding apparatus and themethod therefor, and the image information decoding apparatus and themethod therefor according to the present invention, encoding/decodingcan be efficiently performed by intra-image prediction not only inconnection with the case of 4:2:0 format and YCbCr color space, but alsoin connection with 4:2:2 format, 4:4:4 format, RGB color space and/orXYZ color space, etc.

Still further objects of the present invention and practical meritsobtained by the present invention will become more apparent from thedescription of the embodiments which will be given below with referenceto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing outline of the configuration of aconventional image information encoding apparatus adapted for realizingimage compression by orthogonal transform such as discrete cosinetransform or Karhnen-Loeve transform, etc. and motionprediction/compensation.

FIG. 2 is a block diagram showing outline of the configuration of aconventional image information decoding apparatus corresponding to theabove-mentioned image information encoding apparatus.

FIG. 3 is a view for explaining four intra-prediction modes in JVTCodec.

FIG. 4 is a view showing the state where DC coefficients of four 4×4blocks within 8×8 block are collected to constitute 2×2 block.

FIG. 5 is a block diagram showing outline of the configuration of animage information encoding apparatus according to the present invention.

FIG. 6 is a block diagram showing one example of the configuration ofintra-prediction unit in the image information encoding apparatusaccording to the present invention.

FIG. 7 is a view showing one example of the configuration of orthogonaltransform unit in the image information encoding apparatus according tothe present invention.

FIG. 8 is a view showing the state where DC coefficients of eight 4×4blocks within two 8×8 blocks successive in a longitudinal direction arecollected to constitute 2×4 blocks.

FIG. 9 is a block diagram showing one example of the configuration ofquantization unit in the image information encoding apparatus accordingto the present invention.

FIG. 10 is a block diagram showing one example of the configuration ofinverse-quantization unit in the image information encoding apparatusaccording to the present invention.

FIG. 11 is a block diagram showing one example of the configuration ofinverse-orthogonal transform unit in the image information encodingapparatus according to the present invention.

FIG. 12 is a block diagram showing outline of the configuration of animage information decoding apparatus according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

While practical embodiments to which the present invention is appliedwill now be described in detail with reference to the attached drawings,it should be noted that the present invention is not limited to suchembodiments, but it is a matter of course that various changes ormodifications can be made within the scope which does not depart fromthe gist of the present invention.

(1) Configuration and Operation of the Image Information EncodingApparatus

First, outline of the configuration of the image information encodingapparatus according to the present invention is shown in FIG. 5. Theimage information encoding apparatus 10 comprises, as shown in FIG. 5,an A/D (Analogue/Digital) converting unit 11, an image sorting buffer12, an adder 13, an orthogonal transform unit 14, a quantization unit15, a reversible encoding unit 16, a storage buffer 17, an inversequantization unit 18, an inverse orthogonal transform unit 19, an adder20, a frame memory 21, a motion prediction/compensation unit 22, anintra-prediction unit 23, and a rate control unit 24.

In FIG. 5, the A/D converting unit 11 converts an inputted image signalinto a digital signal. Further, the image sorting buffer 12 performssorting of frames in accordance with GOP (Group of Pictures) structureof image compressed information outputted from the image informationencoding apparatus 10. In this example, the image sorting buffer 12delivers image information of the entirety of frames to the orthogonaltransform unit 14 in regard to images in which intra (intra-image)encoding is performed. The orthogonal transform unit 14 implementsorthogonal transform such as discrete cosine transform or Karhunen-Loevetransform, etc. to the image information to deliver transformcoefficients to the quantization unit 15. The quantization unit 15implements quantization processing to the transform coefficientsdelivered from the orthogonal transform unit 14.

The reversible encoding unit 16 implements reversible encoding such asvariable length encoding or arithmetic encoding, etc. to the quantizedtransform coefficients to deliver the transform coefficients thusencoded to the storage buffer 17 to store them thereinto. The encodedtransform coefficients are outputted as image compressed information.

The behavior (operation) of the quantization unit 15 is controlled bythe rate control unit 24. Moreover, the quantization unit 15 deliversquantized transform coefficients to the inverse quantization unit 18.The inverse quantization unit 18 inverse-quantizes the transformcoefficients thus delivered. The inverse orthogonal transform unit 19implements inverse orthogonal transform processing to theinverse-quantized transform coefficients to generate decoded imageinformation to deliver the information thus generated to the framememory 21 to store them thereinto.

On the other hand, the image sorting buffer 12 delivers imageinformation to the motion prediction/compensation unit 22 in regard toimages in which inter (inter-image) encoding is performed. The motionprediction/compensation unit 22 takes out, from the frame memory 21,image information referred at the same time to implement motionprediction/compensation processing thereto to generate reference imageinformation. The motion prediction/compensation unit 22 delivers thereference image information thus generated to the adder 13. The adder 13converts the reference image information into a difference signalbetween the reference image information and corresponding imageinformation. In addition, the motion compensation/prediction unit 22delivers motion vector information to the reversible encoding unit 16 atthe same time.

The reversible encoding unit 16 implements reversible encodingprocessing such as variable length encoding or arithmetic encoding, etc.to the motion vector information thus delivered to form informationinserted into header portion of image compressed information. It is tobe noted that since other processing are the same as those of imagecompressed information to which intra-encoding is implemented, theexplanation thereof will be omitted.

In this example, in the above-described JVT Codec, in performingintra-encoding, there is employed intra-predictive encoding system ofgenerating prediction images from pixels around block to encodedifferences therebetween. Namely, in regard to images in whichintra-encoding is performed (I picture, I slice, intra macro block,etc.), prediction image is generated from already encoded pixel valuesin the vicinity of pixel block to be encoded so that difference withrespect to the prediction image is encoded. The inverse quantizationunit 18 and the inverse orthogonal transform unit 19 respectivelyinverse-quantize and inverse orthogonally transform the intra-encodedpixels. The adder 20 adds output of the inverse orthogonal transformunit 19 and prediction image used in encoding corresponding pixel blockto deliver added value thus obtained to the frame memory 21 to store itthereinto. In the case of pixel block to be intra-encoded, the intraprediction unit 23 reads out already encoded neighboring pixels storedin the frame memory 21 to generate prediction image. At this time, alsowith respect to intra prediction mode used in generation of predictionimage, reversible encoding processing is implemented thereto at thereversible encoding unit 16 to provide an output in the state includedin image compressed information.

(2) The Part to which the Present Invention is Applied in the ImageInformation Encoding Apparatus

(2-1) Intra Prediction Unit

An example of the configuration of the intra prediction unit 23 is shownin FIG. 6. The intra prediction unit 23 switches prediction technique onthe basis of chroma format signal indicating whether resolution of colorcomponent is that of any one of 4:2:0 format, 4:2:2 format and 4:4:4format, etc., and color space signal indicating whether color space isany one of YCbCr, RGB and XYZ, etc. In this example, the chroma formatsignal and the color space signal are set in advance by external user,etc., and are delivered to the image information encoding apparatus 10.

In the intra prediction unit 23 shown in FIG. 6, the chroma formatsignal and the color space signal are delivered to switches 30, 32. Theswitches 30 and 32 select any one of intra predictors 31 a, 31 b, 31 con the basis of the chroma format signal and the color space signal todeliver an image signal which has been read out from the frame memory 21to the selected intra predictor to output prediction image from theselected intra predictor. The switches 30, 32 select the same intrapredictor. It is to be noted that while explanation has been given inFIG. 6 on the premise that any one of three kinds of intra predictors 31a, 31 b, 31 c is selected, the number of intra predictors, i.e., thenumber of prediction systems may be arbitrarily set.

(2-1-1)

First, the operation of the intra predictor 31 a will be explained. Theintra predictor 31 a serves to perform prediction with 8×8 block beingas unit with respect to an image signal in which the chroma formatsignal indicates 4:2:0 format and color space signal indicates YCbCr. Itis to be noted that since the operation of the intra predictor 31 a isthe same as that of the previously described prior art, the detailedexplanation thereof is omitted.

(2-1-2)

Then, the operation of the intra predictor 31 b will be explained. Alsoat the intra predictor 31 b, four prediction modes of Vertical mode,Horizontal mode, DC mode and Plane prediction mode exist in the intracolor difference prediction mode. The intra predictor 31 b serves toperform prediction with 8×16 block constituted by collecting successivetwo 8×8 blocks in a longitudinal direction within macro block being asunit with respect to an image signal in which chroma format signalindicates 4:2:2 format and color space signal indicates YCbCr. Thetechniques of generating prediction images in accordance with respectivefour prediction modes at the intra predictor 31 b will be explainedbelow.

(a) Vertical Mode (Mode=0)

In the Vertical mode, pixels of adjacent upper side block of colordifference block are copied to allow the pixels thus copied to beprediction image of corresponding block. When pixels of adjacent upperside block are expressed as p[x, −1], prediction image predc of colordifference in this case is represented by the following formula (26). Itis to be noted that this mode can be used only in the case whereadjacent upper side block exists.pred_(c) [x,y]=p[x,−1](x=0 . . . 7,y=0 . . . 15)  (26)

(b) Horizontal Mode (Mode=1)

In the Horizontal mode, pixels of adjacent left side block of colordifference block are copied to allow the pixels thus copied to beprediction image of corresponding block. When pixels of adjacent leftside block are expressed as p[−1, y], prediction image predc of thecolor difference block in this case is represented by the followingformula (27). It is to be noted that this mode can be used only in thecase where adjacent left side block exists.pred_(c) [x,y]=p[−1,y](x=0 . . . 7,y=0 . . . 15)  (27)

(c) DC Mode (Mode=2)

In the DC mode, pixels of adjacent upper and left side blocks of colordifference block are used to allow the mean (average) value thereof tobe prediction image. It is to be noted that in the case where adjacentpixels do not exist, value 128 is used as prediction signal.

Namely, in the case of x, y=0 . . . 3, prediction image predc [x, y] isgenerated by using upper side pixel p[x, −1] and left side pixel p[−1,y] which are adjacent (in this example, x, y=0 . . . 3). Moreparticularly, in four cases of (i) the case where pixel p[x, −1] andp[−1, y] both exist, (ii) the case where pixel p[x, −1] exists and pixelp[−1, y] does not exist, (iii) the case where pixel p[x, −1] does notexist and pixel p[−1, y] exists, and (iv) the case where pixel p[x, −1]and pixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (28) to (31).

$\begin{matrix}\lbrack 17\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 0}^{3}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (28) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (29) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 0}^{3}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (30) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = 128}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (31)\end{matrix}$

Similarly, in the case of x=4 . . . 7, y=0 . . . 3, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=4 . . . 7,y=0 . . . 3). More particularly, in three cases of (i) the case wherepixel p[x, −1] exists, (ii) the case where pixel p[x, −1] does not existand pixel p[−1, y] exists, and (iii) the case where pixel p[x, −1] andpixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (32) to (34).

$\begin{matrix}\lbrack 18\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (32) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 0}^{3}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (33) \\{{{pred}_{c} = 128}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {0\mspace{14mu}\ldots\mspace{14mu} 3}}} \right)} & (34)\end{matrix}$

Similarly, in the case of x=0 . . . 3, y=4 . . . 7, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1,y] which are adjacent (in this example, x=0 . . . 3, y=4. . . 7). More particularly, in three cases of (i) the case where pixelp[−1, y] exists, (ii) the case where pixel p[x, −1] exists and pixelp[−1, y] does not exist, and (iii) the case where pixel p[x, −1] andp[−1, y] do not both exist, prediction images are respectively generatedin accordance with the following formulas (35) to (37).

$\begin{matrix}\lbrack 19\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 4}^{7}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (35) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (36) \\{{{pred}_{c} = 128}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (37)\end{matrix}$

Similarly, in the case of x, y=4 . . . 7, prediction image predc [x, y]is generated by using upper side pixel p[x, −1] and left side pixelp[−1, y] which are adjacent (in this example, x, y=4 . . . 7). Moreparticularly, in four cases of (i) the case where pixel p[x, −1] andpixel p[−1, y] both exist, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, (iii) the case where pixel p[x, −1] doesnot exist and pixel p[−1, y] exists, and (iv) the case where pixel p[x,−1] and pixel p[−1, y] do not both exist, prediction images arerespectively generated in accordance with the following formulas (38) to(41).

$\begin{matrix}\lbrack 20\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 4}^{7}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (38) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (39) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 4}^{7}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (40) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = 128}\left( {x,{y = {4\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (41)\end{matrix}$

Similarly, in the case of x=0 . . . 3, y=8 . . . 11, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=0 . . . 3,y=8 . . . 11). More particularly, in three case of (i) the case wherepixel p[−1, y] exists, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, and (iii) the case where pixel p[x, −1]and pixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (42) to (44).

$\begin{matrix}\lbrack 21\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 8}^{11}{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 11}}} \right)} & (42) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{3}{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\text{}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 11}}} \right)} & (43) \\{{{pred}_{c} = 128}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 11}}} \right)} & (44)\end{matrix}$

Similarly, in the case of x=4 . . . 7, y=8 . . . 11, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=4 . . . 7,y=8 . . . 11). More particularly, in four cases of (i) the case wherepixel p[x, −1] and pixel p[−1, y] both exist, (ii) the case where pixelp[x, −1] exists and pixel p[−1, y] does not exist, (iii) the case wherepixel p[x, −1] does not exist and pixel p[−1, y] exists, and (iv) thecase where pixel p[x, −1] and pixel p[−1, y] do not both exist,prediction images are respectively generated in accordance with thefollowing formulas (45) to (48).

$\begin{matrix}\lbrack 22\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 8}^{11}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{11mu}\ldots\mspace{14mu} 11}}} \right)} & (45) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{11mu}\ldots\mspace{14mu} 11}}} \right)} & (46) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 8}^{11}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 11}}} \right)} & (47) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = 128}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 11}}} \right)} & (48)\end{matrix}$

Similarly, in the case of x=0 . . . 3, y=12 . . . 15, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=0 . . . 3,y=12 . . . 15). More particularly, in three cases of (i) the case wherepixel p[−1, y] exists, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, and (iii) the case where pixel p[x, −1]and pixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (49) to (51)

$\begin{matrix}\lbrack 23\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 12}^{15}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (49) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{3}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\text{}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (50) \\{{{pred}_{c} = 128}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 3}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (51)\end{matrix}$

Similarly, in the case of x=4 . . . 7, y=12 . . . 15, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=4 . . . 7,y=12 . . . 15). More particularly, in four cases of (i) the case wherepixel p[x, −1] and pixel [−1, y] both exist, (ii) the case where pixelp[x, −1] exists and pixel p[−1, y] does not exist, (iii) the case wherepixel p[x, −1] does not exist and pixel p[−1, y] exists, and (iv) thecase where pixel p[x, −1] and pixel p[−1, y] do not both exist,prediction images are respectively generated in accordance with thefollowing formulas (52) to (55).

$\begin{matrix}\lbrack 24\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 12}^{15}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (52) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 4}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (53) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 12}^{15}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 2} \right) ⪢ 2}}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (54) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = 128}\left( {{x = {4\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {12\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)} & (55)\end{matrix}$

Here, in the above-described prediction method, since mean (average)value of eight pixels of upper side block and 16 pixels of left sideblock is simply caused to be prediction image, it is necessary toperform division by 24. Thus, there is the problem that operationquantity becomes many. In view of the above, the prediction method ismodified in a manner as described below to perform division by 16 (=24),thereby making it possible to reduce operation quantity.

Namely, in the case of x, y=0 . . . 7, prediction image predc [x, y] isgenerated by using upper side pixel p[x, −1] and left side pixel p[−1,y] which are adjacent (in this example, x, y=0 . . . 7). Moreparticularly, in four cases of (i) the case where pixel p[x, −1] andpixel p[−1, y] both exist, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, (iii) the case where pixel p[x, −1] doesnot exist and pixel p[−1, y] exists, and (iv) the case where pixel p[x,−1] and pixel p[−1, y] do not both exist, prediction images arerespectively generated in accordance with the following formulas (56) to(59).

$\begin{matrix}\lbrack 25\rbrack & \; \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 0}^{7}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 8} \right) ⪢ 4}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (56) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (57) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 0}^{7}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (58) \\{{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = 128}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 7}}} \right)} & (59)\end{matrix}$

Similarly, in the case of x=0 . . . 7, y=8 . . . 15, prediction imagepredc [x, y] is generated by using upper side pixel p[x, −1] and leftside pixel p[−1, y] which are adjacent (in this example, x=0 . . . 7,y=8 . . . 15). More particularly, in three cases of (i) the case wherepixel p[−1, y] exists, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, and (iii) the case where pixel p[x, −1]and pixel p[−1, y] do not both exist, prediction images are respectivelygenerated in accordance with the following formulas (60) to (62).

$\begin{matrix}\lbrack 26\rbrack & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 8}^{15}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 4} \right) ⪢ 3}} & (60) \\\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 15}}} \right) & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{7}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 4} \right) ⪢ 3}} & (61) \\\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 15}}} \right) & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {128\mspace{14mu}\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {8\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)}} & (62)\end{matrix}$

(d) Plane Prediction Mode (Mode=3)

In the Plane Prediction mode, prediction image is plane-approximatedfrom pixel of left side block and pixel of upper side block which areadjacent of color difference block to allow the prediction image thusobtained to be prediction image of the corresponding block. When pixelsof left and upper side blocks which are adjacent are respectivelyexpressed as p[−1, y] and p[x, −1], prediction image predc of colordifference in this case is represented by the following formula (63).Here, Clip1 in the formula (63) indicates that clipping is performedinto the range from 0 to 255.

$\begin{matrix}\lbrack 27\rbrack & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {{Clip}\; 1\left( {\left( {a + {b \times \left( {x - 3} \right)} + {c \times \left( {y - 7} \right)} + 16} \right) ⪢ 5} \right)}} & (63) \\\left( {{x = {0\mspace{14mu}\ldots\mspace{14mu} 7}},\mspace{14mu}{y = {0\mspace{14mu}\ldots\mspace{14mu} 15}}} \right) & \; \\{where} & \; \\\left\{ \begin{matrix}{a = {16 \times \left( {{p\left\lbrack {{- 1},15} \right\rbrack} + {p\left\lbrack {7,{- 1}} \right\rbrack}} \right)}} \\{b = {\left( {{17 \times H} + 16} \right) ⪢ 5}} \\{c = {\left( {{5 \times V} + 32} \right) ⪢ 6}} \\{H = {\sum\limits_{x^{\prime} = 0}^{3}{\left( {x^{\prime} + 1} \right) \times \left( {{p\left\lbrack {{4 + x^{\prime}},{- 1}} \right\rbrack} - {p\left\lbrack {{2 - x^{\prime}},{- 1}} \right\rbrack}} \right)}}} \\{V = {\sum\limits_{y^{\prime} = 0}^{7}{\left( {y^{\prime} + 1} \right) \times \left( {{p\left\lbrack {{- 1},{8 + y^{\prime}}} \right\rbrack} - {p\left\lbrack {{- 1},{6 - y^{\prime}}} \right\rbrack}} \right)}}}\end{matrix} \right. & \;\end{matrix}$

(2-1-3)

Subsequently, the operation of the intra predictor 31 c will beexplained. Also at the intra predictor 31 c, four prediction modes ofVertical mode, Horizontal mode, DC mode and Plane prediction mode existin the intra color difference prediction mode. The intra predictor 31 cperforms prediction with 16×16 block constituted by collecting four 8×8blocks in longitudinal and lateral directions successive within macroblock being as unit with respect to image signal in which chroma formatsignal indicates 4:4:4 format and color space signal indicates YCbCr,RGB or XYZ. Techniques of generating prediction images in accordancewith respective four prediction modes at the intra predictor 31 c willbe explained.

(a) Vertical Mode (Mode=0)

In the Vertical mode, pixels of adjacent upper side block of colordifference block are copied to allow the pixels thus copied to beprediction image of corresponding block. When pixels of adjacent upperside block are expressed as p[x, −1], prediction image predc of colordifference in this case is represented by the following formula (64). Itis to be noted that this mode can be used only in the case whereadjacent upper side block exists.pred_(c) [x,y]=p[x,−1](x,y=0 . . . 15)  (64)

(b) Horizontal Mode (Mode=1)

In the Horizontal mode, pixels of adjacent left side block of colordifference block are copied to allow the pixels thus copied to beprediction image of the corresponding block. When pixels of adjacentleft side block are expressed as p[−1, y], prediction image predc ofcolor difference block in this case is represented by the followingformula (65). It is to be noted that this mode can be used only in thecase where adjacent left side block exists.pred_(c) [x,y]=p[−1,y](x,y=0 . . . 15)  (65)

(c) DC Mode (Mode=2)

In the DC mode, pixels of upper and lower side blocks which are adjacentof color difference block are used to allow the mean (average) valuethereof to be prediction image. It is to be noted that in the case whereadjacent pixels do not exist, value 128 is used as prediction signal.

Namely, in the case of x, y=0 . . . 15, prediction image predc p[x, y]is generated by using upper side pixel p[x, −1] and left side pixelp[−1, y] which are adjacent (in this example, x, y=0 . . . 15). Moreparticularly, in four cases of (i) the case where pixel p[x, −1] andpixel p[−1, y] both exist, (ii) the case where pixel p[x, −1] exists andpixel p[−1, y] does not exist, (iii) the case where pixel p[x, −1] doesnot exist and pixel p[−1, y] exists, and (iv) the case where pixel p[x,−1] and pixel p[−1, y] do not both exist, prediction images arerespectively generated in accordance with the following formulas (66) to(69).

$\begin{matrix}\lbrack 30\rbrack & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{15}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + {\sum\limits_{y^{\prime} = 0}^{15}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 16} \right) ⪢ 5}} & (66) \\\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 15}}} \right) & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{x^{\prime} = 0}^{15}\;{p\left\lbrack {x^{\prime},{- 1}} \right\rbrack}} + 8} \right) ⪢ {4\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)}}} & (67) \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {\left( {{\sum\limits_{y^{\prime} = 0}^{15}\;{p\left\lbrack {{- 1},y^{\prime}} \right\rbrack}} + 8} \right) ⪢ {4\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)}}} & (68) \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {128\mspace{14mu}\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 15}}} \right)}} & (69)\end{matrix}$

(d) Plane Prediction Mode (Mode=3)

In the Plane Prediction mode, prediction image is plane-approximatedfrom pixel of left side block and pixel of upper side block which areadjacent of color difference block to allow the prediction image thusobtained to be prediction image of corresponding block. When pixels ofleft and upper side blocks which are adjacent are respectively expressedas p[−1, y] and p[x, −1], the prediction image predc of color differencein this case is represented by the following formula (70). Here, Clip1in the formula (70) indicates that clipping into the range from 0 to 255is performed.

$\begin{matrix}\lbrack 31\rbrack & \; \\{{{pred}_{c}\left\lbrack {x,y} \right\rbrack} = {{Clip}\; 1\left( {\left( {a + {b \times \left( {x - 7} \right)} + {c \times \left( {y - 7} \right)} + 16} \right) ⪢ 5} \right)}} & (70) \\\left( {x,{y = {0\mspace{14mu}\ldots\mspace{14mu} 15}}} \right) & \; \\{where} & \; \\\left\{ \begin{matrix}{a = {16 \times \left( {{p\left\lbrack {{- 1},15} \right\rbrack} + {p\left\lbrack {15,{- 1}} \right\rbrack}} \right)}} \\{b = {\left( {{5 \times H} + 32} \right) ⪢ 6}} \\{c = {\left( {{5 \times V} + 32} \right) ⪢ 6}} \\{H = {\sum\limits_{x^{\prime} = 0}^{7}{\left( {x^{\prime} + 1} \right) \times \left( {{p\left\lbrack {{8 + x^{\prime}},{- 1}} \right\rbrack} - {p\left\lbrack {{6 - x^{\prime}},{- 1}} \right\rbrack}} \right)}}} \\{V = {\sum\limits_{y^{\prime} = 0}^{7}{\left( {y^{\prime} + 1} \right) \times \left( {{p\left\lbrack {{- 1},{8 + y^{\prime}}} \right\rbrack} - {p\left\lbrack {{- 1},{6 - y^{\prime}}} \right\rbrack}} \right)}}}\end{matrix} \right. & \;\end{matrix}$

(2-2) Orthogonal Transform Unit

Chroma format signal and color space signal are also delivered to theorthogonal transform unit 14.

One example of the configuration of the orthogonal transform unit 14 isshown in FIG. 7. The orthogonal transform unit 14 switches orthogonaltransform system on the basis of chroma format signal indicating whetherresolution of color component is that of any one of the 4:2:0 format,the 4:2:2 format and the 4:4:4 format, etc., and color space signalindicating whether color space is any one of YCbCr, RGB and XYZ, etc.

At the orthogonal transform unit 14 shown in FIG. 7, the chroma formatsignal and the color space signal are delivered to switches 40, 42. Theswitches 40, 42 select any one of orthogonal transform elements 41 a, 41b, 41 c on the basis of the chroma format signal and the color spacesignal to deliver output from the adder 13 to the selected orthogonaltransform element to output a signal from the selected orthogonaltransform element. The switches 40, 42 select the same orthogonaltransform element. It is to be noted that while explanation will begiven in FIG. 7 on the premise that any one of three kinds of orthogonaltransform elements 41 a, 41 b, 41 c is selected, the number oforthogonal transform elements, i.e., the number of orthogonal transformsystems may be arbitrarily set.

(2-2-1)

First, the operation of the orthogonal transform element 41 a will beexplained. The orthogonal transform element 41 a performs orthogonaltransform with respect to an image signal in which chroma format signalindicates 4:2:0 format and color space signal indicates YCbCr. It is tobe noted that since the operation of the orthogonal transform element 41a is the same as that of the previously described prior art, thedetailed explanation thereof is omitted.

(2-2-2)

Then, the operation of the orthogonal transform element 41 b will beexplained. The orthogonal transform element 41 b performs orthogonaltransform with respect to an image signal in which chroma format signalindicates 4:2:2 format and color space signal indicates YCbCr.

More particularly, after intra-prediction of color difference isperformed, 4×4 integer transform is applied on 4×4 pixel block basiswithin 8×8 blocks. When difference signal obtained by subtractingprediction image from corresponding pixel block is expressed as f4×4,4×4 orthogonal transform processing is represented by the followingformula (71).

$\begin{matrix}\lbrack 32\rbrack & \; \\{f_{4 \times 4} = {T_{4 \times 4} \times F_{4 \times 4} \times T_{4 \times 4}^{T}}} & (71) \\{where} & \; \\{T_{4 \times 4} = \begin{pmatrix}1 & 1 & 1 & 1 \\2 & 1 & {- 1} & {- 2} \\1 & {- 1} & {- 1} & 1 \\1 & {- 2} & 2 & {- 1}\end{pmatrix}} & \;\end{matrix}$

After 4×4 integer transform processing is performed, (0, 0) coefficientsof eight 4×4 blocks within two 8×8 blocks successive in a longitudinaldirection are collected to constitute 2×4 block to apply 2×4 transformprocessing to the 2×4 block. This is because efficiency ofintra-prediction used in color difference is not so high so thatcorrelation is still left between (0, 0) coefficients of adjacent 4×4blocks. In order to further enhance (increase) encoding efficiency bymaking use of the correlation, only (0, 0) coefficients of 4×4 blocksare collected to constitute 2×4 blocks to apply 2×4 transform processingthereto. When block of chroma DC of 2×4 is expressed as fdc 2×4,transform processing with respect to the chroma DC block is representedby the following formula (72).

$\begin{matrix}\lbrack 33\rbrack & \; \\{{fdc}_{2 \times 4}^{\prime} = {T_{v{(4)}} \times {fdc}_{2 \times 4} \times T_{h{(2)}}^{T}}} & (72) \\{where} & \; \\{{T_{v{(4)}} = \begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}}{T_{h{(2)}} = \begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}} & \;\end{matrix}$

(2-2-3)

Subsequently, the operation of the orthogonal transform element 41 cwill be explained. The orthogonal transform element 41 c performsorthogonal transform with respect to an image signal in which chromaformat signal indicates 4:4:4 format and color space signal indicatesYCbCr, RGB or XYZ.

More particularly, 4×4 integer transform of color difference indicating4:4:4 format, YCbCr, RGB or XYZ is performed thereafter to collect 16(0, 0) coefficients within macro block in the same manner as the case ofluminance to constitute 4×4 DC block to apply 4×4 transform processingthereto. This transform processing is represented by the followingformula (73).

$\begin{matrix}\lbrack 34\rbrack & \; \\{{fdc}_{4 \times 4}^{\prime} = {T_{4 \times 4} \times {fdc}_{4 \times 4} \times T_{4 \times 4}^{T}}} & (73) \\{where} & \; \\{T_{4 \times 4} = \begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}} & \;\end{matrix}$

(2-3) Quantization Unit

Chroma format signal and color space signal are also delivered to thequantization unit 15.

An example of the configuration of the quantization unit 15 is shown inFIG. 9. The quantization unit 15 switches quantization system on thebasis of chroma format signal indicating whether resolution of colorcomponent is that of any one of 4:2:0 format, 4:2:2 format and 4:4:4format, etc. and color space signal indicating whether color space isany one of YCbCr, RGB and XYZ, etc.

At the quantization unit 15 shown in FIG. 9, chroma format signal andcolor space signal are delivered to switches 50, 52. The switches 50, 52select any one of quantizers 51 a, 51 b, 51 c on the basis of chromaformat signal and color space signal to deliver an output from theorthogonal transform unit 14 to the selected quantizer to output asignal from the selected quantizer. The switches 50, 52 select the samequantizer. It is to be noted that while explanation will be given inFIG. 9 on the premise that any one of three kinds of quantizers 51 a, 51b, 51 c is selected, the number of quantizers, i.e., the number ofquantization systems may be arbitrarily set.

(2-3-1)

First, the operation of the quantizer 51 a will be explained. Thequantizer 51 a performs quantization with respect to an image signal inwhich chroma format signal indicates 4:2:0 format and color space signalindicates YCbCr. It is to be noted that since the operation of thequantizer 51 a is the same as that of the previously described priorart, the detailed explanation thereof is omitted.

(2-3-2)

Then, the operation of the quantizer 51 b will be explained. Thequantizer 51 b performs quantization with respect to an image signal inwhich chroma format signal indicates 4:2:2 format and color space signalindicates YCbCr.

Here, Hadamard transform used in transform processing of chroma DC inthe case of 4:2:0 format is represented by the following formula (74).

$\begin{matrix}\lbrack 35\rbrack & \; \\\begin{matrix}{{fdc}_{2 \times 4}^{\prime} = {T_{2} \times {fdc}_{2 \times 2} \times T_{2}^{T}}} \\{= {\frac{1}{2}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}{{fdc}_{2 \times 2}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}}}\end{matrix} & (74) \\{where} & \; \\{T_{2} = {\frac{1}{\sqrt{2}}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}} & \;\end{matrix}$

On the other hand, 2×4 transform used in transform processing of chromaDC in the case of 4:2:2 format is represented by the following formula(75).

$\begin{matrix}\lbrack 36\rbrack & \; \\\begin{matrix}{{fdc}_{2 \times 4}^{\prime} = {T_{v{(4)}} \times {fdc}_{2 \times 4} \times T_{h{(2)}}^{T}}} \\{= {\frac{1}{2\sqrt{2}}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}{f_{2 \times 4}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}}}\end{matrix} & (75) \\{where} & \; \\{{T_{v{(4)}} = \begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}}{T_{h{(2)}} = \begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}} & \;\end{matrix}$

Accordingly, normalization coefficient by transform processing in the4:2:0 format is ½, whereas normalization coefficient by transformprocessing in the 4:2:2 format is ½√2. However, since real numberoperation is included in this case, 2×4 transform is simplified asindicated by the following formula (76).

$\begin{matrix}\lbrack 37\rbrack & \; \\\begin{matrix}{{fdc}_{2 \times 4}^{\prime} = {T_{v{(4)}} \times {fdc}_{2 \times 4} \times T_{h{(2)}}^{T}}} \\{= {{\frac{1}{2\sqrt{2}}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}{{fdc}_{2 \times 4}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}} \approx}} \\{\frac{1}{4}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}{{fdc}_{2 \times 4}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}}\end{matrix} & (76)\end{matrix}$

Since the normalization coefficients are calculated together with scalein quantization, it is necessary to change the quantization method in amanner as described below in the case of transform processing of 4:2:2format.

When quantized DC coefficient is Qf′[ij], quantized coefficient valuesof 2×4 chroma DC block are given by, e.g., the following formula (77).Here, r in the formula (77) is parameter for changing roundingprocessing. It is to be noted that since quantization with respect to ACcoefficients is the same as that in the case of the 4:2:0 format, theexplanation thereof will be omitted.Qfdc′[i,j]=(fdc′[i,j]×Q(QP _(c)%6,0,0)+r)>>(15+QPc/6)(i=0 . . . 1,j=0 .. . 3)  (77)

(2-3-3)

Subsequently, the operation of the quantizer 51 c will be explained. Thequantizer 51 c performs quantization with respect to an image signal inwhich chroma format signal indicates 4:4:4 format and color space signalindicates YCbCr, RGB or XYZ.

Here, Hadamard transform used in transform processing of chroma DC isrepresented by the following formula (78). Accordingly, in this case,the normalization coefficient of transform processing becomes equal to¼.

$\begin{matrix}\lbrack 39\rbrack & \; \\\begin{matrix}{{fdc}_{4 \times 4}^{\prime} = {T_{4} \times {fdc}_{4 \times 4} \times T_{4}^{T}}} \\{= {\frac{1}{4}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}{{fdc}_{4 \times 4}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}}}}\end{matrix} & (78) \\{where} & \; \\{T_{4} = {\frac{1}{2}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}}} & \;\end{matrix}$

When quantized DC coefficient is Qf′[i,j], quantized coefficient valueof 4×4 chroma DC block is given by, e.g., the following formula (79).Here, r in the formula (79) is parameter for changing roundingprocessing.Qfdc′[i,j]=(fdc′[i,j]×Q(QP _(c)%6,0,0)+r)>>(15+QP _(c)/6)(i,j=0 . . .3)  (79)

(2-4) Inverse Quantization Unit

Chroma format signal and color space signal are also delivered to theinverse quantization unit 18.

One example of the configuration of the inverse quantization unit 18 isshown in FIG. 10. The inverse quantization unit 18 switches inversequantization system on the basis of chroma format signal indicatingwhether resolution of color component is that of any one of 4:2:0format, 4:2:2 format and 4:4:4 format, etc. and color space signalindicating whether color space is any one of YCbCr, RGB and XYZ, etc.

In the inverse quantization unit 18 shown in FIG. 10, chroma formatsignal and color space signal are delivered to switches 60, 62. Theswitches 60, 62 select any one of inverse quantizers 61 a, 61 b, 61 c onthe basis of the chroma format signal and the color space signal todeliver output from the quantization unit 15 to the selectedinverse-quantizer to output a signal from the selectedinverse-quantizer. The switches 60, 62 select the sameinverse-quantizer. It is to be noted that while explanation will begiven in the FIG. 10 on the premise that any one of three kinds ofinverse-quantizers 61 a, 61 b, 61 c is selected, the number ofinverse-quantizers, i.e., the number of inverse-quantization systems maybe arbitrarily set.

(2-4-1)

First, the operation of the inverse-quantizer 61 a will be explained.The inverse-quantizer 61 a performs inverse-quantization with respect toan image signal in which chroma format signal indicates 4:2:0 format andcolor space signal indicates YCbCr. It is to be noted that since theoperation of the inverse-quantizer 61 a is the same as that of thepreviously described prior art, the detailed explanation thereof will beomitted.

(2-4-2)

Then, the operation of the inverse-quantizer 61 b will be explained. Theinverse-quantizer 61 b performs inverse quantization with respect to animage signal in which chroma format signal indicates 4:2:2 format andcolor space signal indicates YCbCr.

More particularly, when inverse-quantized DC coefficient is fdc″,inverse-quantized DC coefficient value of 2×2 chroma DC block isrepresented by the following formula (80) in the case where QPc is 6(six) or more, and is represented by the following formula (81) in thecase where QPc is less than 6 (six). It is to be noted that sinceinverse-quantization with respect to AC coefficients is the same as thatin the case of 4:2:0 format, the explanation thereof will be omitted.fdc″[i,j]=(fdc′[i,j]×Q(QP _(c)%6,0,0))<<(QP _(c)/6−2)(i=0 . . . 1,j=0 .. . 3)  (80)fdc″[i,j]=(fdc′[i,j]×Q(QP _(c)%6,0,0))>>(2−QP _(c)/6)(i=0 . . . 1,j=0 .. . 3)  (81)

(2-4-3)

Then, the operation of the inverse-quantizer 61 c will be explained. Theinverse-quantizer 61 c performs inverse quantization with respect to animage signal in which chroma format signal indicates 4:4:4 format andcolor space signal indicates YCbCr, RGB or XYZ.

More particularly, when inverse-quantized DC coefficient is fdc″,inverse-quantized coefficient value of 4×4 chroma DC block isrepresented by the following formula (82) in the case where QPc is 6(six) or more, and is represented by the following formula (83) in thecase where QPc is less than 6 (six). It is to be noted that sinceinverse quantization with respect to AC coefficients is the same as thatin the case of 4:2:0 format, the explanation thereof will be omitted.fdc″[i,j]=(fdc′[i,j]×Q(QP _(c)%6,0,0))<<(QP _(c)/6−2)(i,j=0 . . .3)  (82)fdc″[i,j]=(fdc′[i,j]×Q(QP _(c)%6,0,0))>>(2−QP _(c)/6)(i,j=0 . . .3)  (83)

(2-5) Inverse Orthogonal Transform Unit

Chroma format signal and color space signal are also delivered to theinverse orthogonal transform unit 19.

One example of the configuration of the inverse orthogonal transformunit 19 is shown in FIG. 11. The inverse orthogonal transform unit 19switches inverse orthogonal transform system on the basis of chromaformat signal indicating whether resolution of color component is thatof any one of 4:2:0 format, 4:2:2 format and 4:4:4 format, etc. andcolor space signal indicating whether color space is any one of YCbCr,RGB and XYZ, etc.

In the inverse orthogonal transform unit 19 shown in FIG. 11, chromaformat signal and color space signal are delivered to switches 70, 72.The switches 70, 72 select any one of inverse orthogonal transformelements 71 a, 71 b, 71 c on the basis of the chroma format signal andthe color space signal to deliver an output from the inversequantization unit 18 to the selected inverse orthogonal transformelement to output a signal from the selected inverse orthogonaltransform element. The switches 70, 72 select the same inverseorthogonal transform element. It is to be noted that while explanationwill be given in the FIG. 11 on the premise that any one of three kindsof inverse orthogonal transform elements 71 a, 71 b, 71 c is selected,the number of inverse orthogonal transform elements, i.e., the number ofinverse orthogonal transform systems may be arbitrarily set.

(2-5-1)

First, the operation of the inverse orthogonal transform element 71 awill be explained. The inverse-orthogonal transform element 71 aperforms inverse orthogonal transform with respect to an image signal inwhich chroma format signal indicates 4:2:0 format and color space signalindicates YCbCr. It is to be noted that since the operation of theinverse orthogonal transform element 71 a is the same as that of thepreviously described prior art, the detailed explanation thereof will beomitted.

(2-5-2)

Then, the operation of the inverse orthogonal transform element 71 bwill be explained. The inverse orthogonal transform element 71 bperforms inverse orthogonal transform with respect to an image signal inwhich chroma format signal indicates 4:2:2 format and color space signalindicates YCbCr.

More particularly, 2×4 inverse transform processing is applied to 2×4 DCblock. When inverse-transformed 2×4 chroma DC block is expressed asfdc2×4′″, inverse transform with respect to the chroma DC block isrepresented by the following formula (84).

$\begin{matrix}\lbrack 43\rbrack & \; \\{{fdc}_{2 \times 4}^{\prime\prime\prime} = {T_{v{(4)}} \times {fdc}_{2 \times 4}^{''} \times T_{h{(2)}}^{T}}} & (84) \\{where} & \; \\{{T_{v{(4)}} = \begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}}{T_{h{(2)}} = \begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix}}} & \;\end{matrix}$

With the chroma DC coefficient being as (0, 0) coefficients of 4×4 blockas shown in FIG. 8, inverse transform processing of respective 4×4blocks is performed. When respective coefficients of 4×4 blocks in whichfdc2×4′″ which is inverse-transformed chroma DC is caused to be (0, 0)coefficient are expressed as F′4×4 and decoded difference signal atinverse transformed 4×4 block is expressed as F″4×4, inverse transformprocessing is represented by the following formula (85).

$\begin{matrix}\lbrack 44\rbrack & \; \\{F_{4 \times 4}^{''} = {T_{4 \times 4} \times F_{4 \times 4}^{\prime} \times T_{4 \times 4}^{T}}} & (85) \\{where} & \; \\{T_{4 \times 4} = \begin{pmatrix}1 & 1 & 1 & 1 \\2 & 1 & {- 1} & {- 2} \\1 & {- 1} & {- 1} & 1 \\1 & {- 2} & 2 & {- 1}\end{pmatrix}} & \;\end{matrix}$

(2-5-3)

Subsequently, the operation of the inverse orthogonal transform element71 c will be explained. The inverse orthogonal transform element 71 cperforms inverse orthogonal transform with respect to an image signal inwhich chroma format signal indicates 4:4:4 format and color space signalindicates YCbCr, RGB or XYZ.

More particularly, 4×4 inverse transform processing is applied to 4×4 DCblocks. When inverse-transformed 4×4 chroma DC block is expressed asfdc4×4′″, inverse transform processing with respect to the chroma DCblock is represented by the following formula (86).

$\begin{matrix}\lbrack 45\rbrack & \; \\{{fdc}_{4 \times 4}^{\prime\prime\prime} = {T_{4} \times {fdc}_{4 \times 4}^{''} \times T_{4}^{T}}} & (86) \\{where} & \; \\{T_{4} = {\frac{1}{2}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & {- 1} & 1 & {- 1}\end{pmatrix}}} & \;\end{matrix}$

With this chroma DC coefficient being as (0, 0) coefficient of 4×4 blockof AC coefficients, inverse transform processing of respective 4×4blocks is performed. When respective coefficients of 4×4 blocks in whichfdc4×4′″ which is inverse-transformed chroma DC is caused to be (0, 0)coefficient are expressed as F′4×4, and decoded difference signal atinverse-transformed 4×4 block is expressed as F″4×4, inverse transformprocessing is represented by the following formula (87).

$\begin{matrix}\lbrack 46\rbrack & \; \\{F_{4 \times 4}^{''} = {T_{4 \times 4} \times F_{4 \times 4}^{\prime} \times T_{4 \times 4}^{T}}} & (87) \\{where} & \; \\{T_{4 \times 4} = \begin{pmatrix}1 & 1 & 1 & 1 \\2 & 1 & {- 1} & {- 2} \\1 & {- 1} & {- 1} & 1 \\1 & {- 2} & 2 & {- 1}\end{pmatrix}} & \;\end{matrix}$

(2-6) Other Block

The chroma format signal and the color space signal are also deliveredto the reversible encoding unit 16, at which variable length encoding orarithmetic encoding of such signals is performed. The signals thusobtained are outputted in the state included in image compressedinformation.

The chroma format signal and the color space signal are encoded by,e.g., syntax as described below.

seq_parameter_set_rbsp( ){ :  chroma_format_idc u(2)  color_space_idcu(2) : }

Here, syntax encoded as u(2) is encoded by variable length code of,e.g., “001x1x0”. Among them, x1 and x0 correspond to 2 (two) bits ofsyntax to be encoded.

(3) Configuration and Operation of the Image Information DecodingApparatus

Outline of the configuration of an image information decoding apparatuscorresponding to the above-described image information encodingapparatus 10 is shown in FIG. 12. As shown in FIG. 12, the imageinformation decoding apparatus 80 comprises a storage buffer 81, areversible decoding unit 82, an inverse quantization unit 83, an inverseorthogonal transform unit 84, an adder 85, an image sorting buffer 86, aD/A (Digital/Analogue) converting unit 87, a motionprediction/compensation unit 88, a frame memory 89, and an intraprediction unit 90.

In FIG. 12, an image compressed information serving as input is firststored into the storage buffer 81, and is then transferred to thereversible decoding unit 82. The reversible decoding unit 82 performsprocessing such as variable length decoding or arithmetic decoding, etc.on the basis of a predetermined format for image compressed information.Moreover, in the case where corresponding frame is inter-encoded frame,the reversible decoding unit 82 also decodes motion vector informationstored at header portion of the image compressed information to transferthe decoded information thus obtained to the prediction/compensationunit 88. Further, the reversible decoding unit 82 decodes chroma formatsignal and color space signal to deliver decoded signals thus obtainedto the inverse quantization unit 83, the inverse orthogonal transformunit 84 and the intra prediction unit 90.

Quantized transform coefficients serving as output of the reversibledecoding unit 82 are delivered to the inverse quantization unit 83, atwhich they are outputted as transform coefficients. The inverseorthogonal transform unit 84 implements reversible transform such asinverse discrete cosine transform or inverse Karhunen-Loeve transform,etc. to the transform coefficients on the basis of a predeterminedformat for image compressed information. In the case where correspondingframe is intra-encoded frame, image information to which inverseorthogonal transform processing has been implemented is stored into theimage sorting buffer 86, and is outputted after undergone D/A convertingprocessing.

Here, in the case where corresponding frame or macro block isintra-encoded frame or macro block, decoding processing is performed byusing the same inverse quantization method, inverse orthogonal transformmethod and intra prediction method as those as described above on thebasis of the chroma format signal and the color space signal which havebeen decoded at the reversible decoding unit 82.

On the other hand, in the case where corresponding frame isinter-encoded frame, reference image is generated on the basis of motionvector information to which reversible decoding processing has beenimplemented and image information stored in the frame memory 89. Thereference image thus generated and output of the inverse orthogonaltransform unit 84 are synthesized at the adder 85. Since otherprocessing are the same as those of intra-encoded frame, the explanationthereof will be omitted.

It is to be noted that while the present invention has been described inaccordance with certain preferred embodiments thereof illustrated in theaccompanying drawings and described in the above description in detail,it should be understood by those ordinarily skilled in the art that theinvention is not limited to embodiments, but various modifications,alternative constructions or equivalents can be implemented withoutdeparting from the scope and spirit of the present invention as setforth by appended claims.

Industrial Applicability

The present invention can efficiently perform encoding processing byusing intra-image predictive encoding processing not only with respectto the case of input image signal in which corresponding frame is 4:2:0format and color space is YCbCr, but also with respect to the case ofinput image signal in which corresponding format is 4:2:2 format or4:4:4 format, and color space is RGB or XYZ, etc.

The invention claimed is:
 1. An image information decoding apparatus,comprising: a processor; an inverse quantization unit configured by theprocessor to: perform an inverse quantization of an encoded image inaccordance with an inverse quantization scaling factor, the encodedimage corresponding to a chroma signal; and generate inversequantization coefficients corresponding to the chroma signal; an inversetransformation unit configured by the processor to perform an inversetransformation of the inverse quantized coefficients and generate adecoded image corresponding to the chroma signal based on an output ofthe inverse transformation; and an intra-image prediction unitconfigured by the processor to: perform intra prediction of the decodedimage in an intra DC prediction mode; and generate, when the chromasignal format has a 4:4:4 format, a prediction image corresponding tothe chroma signal by: dividing a block of 16×16 pixels into four unitblocks of 8×8 pixels arranged in longitudinal and lateral directionswithin the block of 16×16 pixels; and calculating, for each of the unitblocks of 8×8 pixels, mean pixel values using pixel values of verticaland horizontal pixels disposed adjacent to the block of 16×16 pixels,wherein the inverse quantization unit is further configured by theprocessor to determine the inverse quantization scaling factor based ona normalization coefficient of the inverse transformation and a blocksize of the inverse transformation.
 2. The image information encodingapparatus of claim 1, wherein: the vertical pixels are disposed along afirst longitudinal edge of the block of 16×16 pixels; and the horizontalpixels are disposed along a first lateral edge of the block of 16×16pixels.
 3. The image information encoding apparatus of claim 2, wherein:the four unit blocks comprise first, second, third, and fourth unitblocks; portions of the first unit block are disposed adjacent tocorresponding portions of the vertical and horizontal pixels; at leastportion of the second unit block is disposed adjacent to a correspondingportion of the horizontal pixels; and at least portion of the third unitblock is disposed adjacent to a corresponding portion of the verticalpixels.
 4. The image information encoding apparatus of claim 3, whereinthe intra-image prediction unit is further configured by the processorto calculate at least one mean pixel value for the fourth unit blockbased on (i) the portion of the horizontal pixels disposed adjacent tothe second unit block, and (ii) the portion of the vertical pixelsdisposed adjacent to the third unit block.
 5. The image informationencoding apparatus of claim 3, wherein the intra-image prediction unitis further configured by the processor to: calculate at least one meanpixel value for the second unit block based on (i) the portion of thehorizontal pixels disposed adjacent to the second unit block, and (ii)the portion of the vertical pixels disposed adjacent to the first unitblock; and calculate at least one mean pixel value for the third unitblock based on (i) the portion of the horizontal pixels disposedadjacent to the first unit block, and (ii) the portion of the verticalpixels disposed adjacent to the third unit block.
 6. The imageinformation encoding apparatus of claim 3, wherein the intra-imageprediction unit is further configured by the processor to calculate atleast one mean pixel value for the first unit block based on theportions of the horizontal and vertical pixels disposed adjacent to thefirst unit block.
 7. The image information encoding apparatus of claim1, wherein the inverse quantization unit is further configured by theprocessor to compute a square of a scaling factor for the inversetransformation.
 8. The image information encoding apparatus of claim 1,wherein the inverse quantization unit is further configured by theprocessor to compute a product of first and second scaling factors, thefirst scaling factor corresponding to a first transformation applied toa vertical basis vector, and the second scaling factor corresponding toa second transformation applied to a horizontal basis vector.
 9. Theimage information encoding apparatus of claim 1, wherein: the inversequantization scaling factor comprises an irrational number; and theinverse quantization unit is further configured by the processor to:compute an approximation to the inverse quantization unit, theapproximation comprising a rational number; and perform the inversequantization of an encoded image in accordance with the approximation tothe inverse quantization scaling factor.
 10. A computer-implementedimage information decoding method, comprising: performing an inversequantization of an encoded image in accordance with an inversequantization scaling factor, the encoded image corresponding to a chromasignal; generating inverse quantization coefficients corresponding tothe chroma signal; performing an inverse transformation of the inversequantized coefficients; generating a decoded image corresponding to thechroma signal based on an output of the inverse transformation;performing intra prediction of the decoded image; and generating, whenthe chroma signal format is has a 4:4:4 format, a prediction imagecorresponding to the chroma signal by: dividing a block of 16×16 pixelsinto four unit blocks of 8×8 pixels arranged in longitudinal and lateraldirections within the block of 16×16 pixels; and calculating, for eachof the unit blocks of 8×8 pixels, mean pixel values using pixel valuesof vertical and horizontal pixels disposed adjacent to the block of16×16 pixels, wherein performing the inverse quantization comprisesdetermining the inverse quantization scaling factor based on anormalization coefficient of the inverse transformation and a block sizeof the inverse transformation.
 11. A tangible, non-transitorycomputer-readable storage medium storing instructions which, whenexecuted by at least one processor, cause the at least one processor toperform a method, comprising: performing an inverse quantization of anencoded image in accordance with an inverse quantization scaling factor,the encoded image corresponding to a chroma signal; generating inversequantization coefficients corresponding to the chroma signal; performingan inverse transformation of the inverse quantized coefficients;generating a decoded image corresponding to the chroma signal based onan output of the inverse transformation; performing intra prediction ofthe decoded image; and generating, when the chroma signal format is hasa 4:4:4 format, a prediction image corresponding to the chroma signalby: dividing a block of 16×16 pixels into four unit blocks of 8×8 pixelsarranged in longitudinal and lateral directions within the block of16×16; and calculating, for each of the unit blocks of 8×8 pixels, meanpixel values using pixel values of vertical and horizontal pixelsdisposed adjacent to the block of 16×16 pixels, wherein performing theinverse quantization comprises determining the inverse quantizationscaling factor based on a normalization coefficient of the inversetransformation and a block size of the inverse transformation.